1. Field of the Invention
The present invention relates to a method of manufacturing a thin-film magnetic head.
2. Related Background of the Invention
Recently, as hard disk drives (HDD) have been attaining a higher density, magnetic heads with a higher sensitivity and a higher output have been in demand. For responding to such a demand, a thin-film magnetic head comprising a magnetoresistive device (hereinafter referred to as MR device) utilizing a spin-valve film, which is one of devices exhibiting a giant magnetoresistive effect, has been proposed (see, for example, Japanese Patent Publication No. HEI 8-21166 and Japanese Patent Application Laid-Open No. HEI 6-236527). The spin-valve film comprises a sandwich structure in which two ferromagnetic layers are magnetically separated from each other by a nonmagnetic layer. An antiferromagnetic layer is laminated on one of the ferromagnetic layers, so that an exchange-coupling magnetic field generated in their interface is applied to this ferromagnetic layer (the layer to be pinned, which will be referred to as pinned layer in this specification). Magnetic fields to be magnetically reversed differ between the pinned layer receiving the exchange-coupling magnetic field and the other ferromagnetic layer (referred to as free layer in the specification) not receiving the exchange-coupling magnetic field. Therefore, magnetization directions of the two ferromagnetic layers holding the nonmagnetic layer change from parallel to nonparallel, whereby electrical resistivity shifts greatly, thus yielding a giant magnetoresistive effect.
For improving the reliability of the thin-film magnetic head, it is necessary for the antiferromagnetic layer and the pinned layer to exhibit a sufficiently high exchange-coupling force. It has therefore been known to use PtMn alloys (see, for example, Japanese Patent Application Laid-Open No. HEI 9-147325) and NiMn alloys (see, for example, Japanese Patent Application Laid-Open Nos. HEI 9-63021 and HEI 9-50611), which yield a very strong exchange-coupling force, as a material for the antiferromagnetic layer.
Meanwhile, the thin-film magnetic head is required to read recording media in which information is recorded with a higher density. This necessitates so-called gap narrowing in which the gap between a pair of magnetic shield layers disposed at positions holding the spin-valve film therebetween in the thin-film magnetic head is narrowed. Among the layers disposed between the magnetic shield layers, the insulating layer is hard to make thinner than that currently available. Therefore, it is necessary for the spin-valve film to reduce the thickness. For thinning the spin-valve film, it will be effective if the thickness of the antiferromagnetic layer, which is thicker than the other layers, is reduced.
When a PtMn alloy or NiMn alloy, which is an ordered alloy (a material requiring an ordered atom arrangement in order to exhibit an antiferromagnetic characteristic), is used as a material for the antiferromagnetic layer, a thickness of 10 nm or more is necessary for attaining sufficient exchange coupling and heat resistance characteristics, which cannot respond to the demand for gap narrowing. It has therefore been known to use IrMn alloys (see, for example, Japanese Patent Application Laid-Open Nos. HEI 6-76247 and HEI 9-148132), RuRhMn alloys (see, for example, Japanese Patent Application Laid-Open Nos. HEI 10-242544), and the like, which can attain a sufficient exchange-coupling force even at a small thickness of 10 nm or less, as a material for the antiferromagnetic layer.